Calcium-activated chloride channels (Clca) are widely expressed in numerous cells including epithelial, neuronal, cardiac and smooth muscle cells (SMC). CICa have been implicated in many important cellular functions such as epithelial secretion, membrane excitability in neurons and cardiac muscle as well as regulation of smooth muscle vascular tone. As a result of CICa expression in pulmonary artery smooth muscle cells (PASMC), there is a possibility that these channels may participate in the etiology of various forms of pulmonary hypertension (PH). Recent work by our group has provided evidence for the modulation of calcium-activated chloride currents (Icuca)) through phoshorylation and dephosphorylation by calmodulin- dependent protein kinase II (CaMKII) and Ca2+dependent Calcineurin (CaN;PP2B) respectively in arterial SMC. As a result of the serine/threonine phosphatase CaN involvement in up-regulation of Clca conductance, it is possible that there may be other phophatases contributing in up-regulation their activity as well. In rabbit pulmonary artery SMCs, the major goals of this research project are to: 1) determine the relative role of CaMKII and CaN in the regulation of CICa channels under static and dynamic intracellular calcium levels;2) determine the structural determinants conferring specificity of CaN Aa over CaN A(3 in the regulation of CICa;and 3) examine the possible involvement of other serine/threonine phosphatases (PP1/PP2A) in the modulation of lCi(ca)- To accomplish this task, a variety of techniques will be implemented, including the use of pharmacological agents to inhibit protein phosphatases under whole-cell patch clamp conditions in rabbit PASMC to determine the relative contribution of PP1 and PP2A in CICa conductance. This technique will also prove to be useful in determining whether CaN and the other(s) ser/thr phosphatases target a common or distinct phosphorylation site to modulate Cardiovascular disease (CVD) remains to be one of the largest killers in the United States. According to the American Heart Association, in 2003 CVD was the underlying cause of death for more than 37% of all deaths in the United States. Since ion channels play an important role in the regulation of vascular tone, it is our hope that a better understanding of the underlying mechanisms of ion channels (like Clca) in the cardiovascular system will lead to novel vascular targets for the development of new drugs to improve the conditions of patients suffering from CVDs such as PH, stroke, myocardial angina and infarctions.